Stung by an election defeat, Tony Blair shuffled his Cabinet on Friday and replaced Foreign Secretary Jack Straw in an attempt to save his own political future and shore up support to tackle crises in Iran and Iraq.

Straw had privately expressed doubts about the Iraq war to his boss and publicly took a different stance on Iran. He described military action against Tehran as "inconceivable," something neither Blair nor President Bush would say, and called reports that the Bush administration has contingency plans for a tactical nuclear strike "nuts."

Margaret Beckett, a Blair loyalist who has been serving as environment secretary, takes over the Foreign Office, becoming Britain's first female foreign secretary. Blair's official spokesman said the change did not mean a shift in foreign policy.

Two ministers at the center of a series of recent government woes were also fired or demoted.

But critics said it is Blair himself who should step aside after voters deserted his Labour Party in local council elections Thursday. The results — Labour won 26 percent of the vote to the Tories' 40 percent — were widely seen as a referendum on Blair and his troubled government.

"It'll take far more than a reshuffle," declared opposition Conservative leader David Cameron, whose long-sidelined party was reinvigorated by its strongest electoral showing since 1992. "What we need in this country is a replacement of the government."

Nevertheless, Blair's Cabinet shake-up was his biggest ever and an effort to reassert his dwindling political authority.

Home Secretary Charles Clarke, embroiled in a politically damaging furor over the failure to deport foreign criminals, lost his job and turned down other Cabinet posts, deciding instead to leave the government.

Blair had defended Clarke over the prisoner controversy, but said Friday: "I felt that it was very difficult, given the level of genuine public concern, for Charles to continue."

Deputy Prime Minister John Prescott kept his title despite an admission of an extramarital affair with his secretary — and tabloid reports that the two had trysts in Prescott's government office. But he was stripped of the responsibilities of his department, which include housing and planning.

In other changes, John Reid left his post as defense secretary to replace Clarke, and Des Browne left the Treasury to head the defense ministry.

The appointment of the 63-year-old Beckett came as a surprise. She is a veteran politician and loyal to Blair, but has little experience in foreign affairs beyond her participation in international climate change talks.

In August 2002, though, Beckett was one of the most senior critics of a prospective U.S.-led military intervention in Iraq, raising concerns about the impact an invasion would have on the Iraqi population.

Straw was moved to the far less exalted job of leader of the House of Commons and takes responsibility for overhauling the House of Lords and campaign finance reform, two big issues.

Secretary of State Condoleezza Rice, who had joined Straw on a trip to Baghdad last month, called to wish him well. "She has had an excellent working relationship with him" and the two will remain friends, State Department spokesman Sean McCormack said, adding that Rice looks forward to working with Beckett and expects to talk with her soon.

Labour's drubbing at the polls came after weeks of relentlessly negative headlines over a series of government scandals.

News in March that Labour had accepted millions of dollars in secret loans from wealthy backers created a furor, and Blair denied allegations that he gave nominations to the House of Lords in exchange for financial backing of the party.

More recently, Clarke announced last week that officials had failed to screen more than 1,000 foreign criminals for deportation before releasing them from prison. The next day, Prescott acknowledged the extramarital affair.

The government's troubles have prompted calls that Blair step aside soon and let his likely successor, Treasury chief Gordon Brown, take over as prime minister. The poor election showing has only increased the pressure.

Blair, who turns 53 on Saturday, was re-elected to a third term last year with a drastically reduced majority, has said he will not run again but intends to serve his full third term.

A group of Labour lawmakers were drafting a letter urging Blair to outline a "firm and fixed timetable" for an early departure from office, Channel 4 News reported. It did not identify the legislators, but said they claimed 50 supporters in the House of Commons.

"There are a lot of grumblings of discontent within the party about Tony Blair's leadership," said Martin Bright, political editor at the left-leaning New Statesman magazine.

Anthony Seldon, a Blair biographer, said the prime minister realized he had to carry out a bold shake-up if he was to win enough time in office to push through his agenda on health, pensions and other domestic issues.

"This is his last chance to get it right," Seldon said. "He realizes time is running out."

Blair's new team will face an emboldened opposition.

The Conservatives made a net gain of 310 seats and Labour lost a net of 306, out of 4,360 seats up for grabs on 176 local councils across England. The far-right British National Party won 27 seats.

The outcome will strengthen Cameron's hand as he continues overhauling his party. He wants to give the Tories a more moderate image and make them electable again nationally. The last time the Conservatives controlled Parliament was 1997, when a bevy of sex and corruption scandals helped bring down Prime Minister John Major.